Abnormalities associated with inflammation comprise a large, unrelated group of disorders which underlie a variety of human diseases. Examples of disorders associated with inflammation include asthma, chronic inflammation, and autoimmune diseases including rheumatoid arthritis. Chronic inflammation is a pathological condition characterised by concurrent active inflammation, tissue destruction, and attempts at repair. Rheumatoid arthritis (RA) is a chronic, systemic autoimmune disorder that causes the immune system to attack the joints, where it causes inflammation (arthritis) and destruction. It can also damage some organs, such as the lungs and skin. It can be a disabling and painful condition, which can lead to substantial loss of functioning and mobility. It is diagnosed with blood tests (especially a test called rheumatoid factor) and X-rays.
The inflammatory reaction observed in autoimmune disease involves both cellular and soluble players. The cause of RA is not known. It involves complex interactions of various cells, cytokines and enzymes. The disease begins when an inciting antigen gains access to the joint, triggering an immune response. The antigenic stimulus activates CD4+ lymphocytes (T-cells). Once CD4+ T-cells become activated, a complex cascade of biological events take place including stimulation of macrophages, B-cells, fibroblasts, chondrocytes and osteoclasts. Activated macrophages secrete cytokines, such as interleukin-1 (IL-1), IL-6, IL-8, IL-15 and tumor necrosis factor-α (TNF-α) (Martinez et al., 2008).
Interleukin-4 (IL-4) is secreted by CD4+ T-cells (Th2 cells). It is a pleiotropic cytokine, acting on various cell types and tissues. Its action on immune cells results in activation and growth of B cells, IgG and IgE production, MHC class II induction, growth and survival of T cells, Th2 differentiation, enhancement of mast cell growth, enhancement of IL-2 and IL-12-induced interferon-γ (INF-γ) secretion in NK cells, downregulation of C5a and C3a in monocytes and Mo-derived dendritic cells and inhibition of macrophage activation (Agnello et al., 2003; Szehedi et al., 2003; Roland, 2003).
The structure of recombinant human IL-4 has been determined by both NMR and X-ray diffraction methods in several laboratories. It has a classical 4 helix bundle cytokine structure (Muller et al., 1995). IL-4, like other cytokines, exerts its biological activity by binding to the receptors on the cell surface. One receptor complex is composed of two components, the IL-4R α chain (IL-4Rα) and the IL-2R γ chain (γc, shared by the cytokines IL-2, IL-7, IL-9, IL-15 and IL-21), denoted type I IL-4R, whereas the other receptor complex is composed of IL-4Rα and the IL13 α chain (IL-13Rα1), called type II IL-4R. As γ c is expressed on most hematopoietic and immune cells, IL-4 is assumed to act on these cells through type I IL-4R. In contrast, expression of IL-13Rα1 is limited to some lineages such as B cells in hematopoietic and immune cells, but ubiquitously detected on non-immune cells (Izuhara et al., 2002). Thus IL4 acts on non-immune cells through type II IL-4R/IL-13R.
Binding IL-4 to its receptor a chain (IL-4Ra) is a crucial event for the generation of a Th2-dominated early immune response. The crystal structure of the intermediate complex between human IL-4 and IL4-BP was determined at 2.3 Å Resolution (PDB ID: 1IAR). It reveals a novel spatial orientation of the two proteins, a small but unexpected conformational change in the receptor-bound IL-4, and an interface with three separate clusters of trans-interacting residues (Hage et al., 1999). Crystal structure of the Il4-Il4r-common gamma ternary complex has recently been solved (PDB ID: 3BPL; LaPorte et al., 2008).
Recombinant IL-4 has been through several clinical trials. IL-4 has been shown to be beneficial in patients with psoriasis, effectively correcting imbalances in immune functions (Martin 2003). The safety and tolerability of Escherichia coli-derived recombinant human interleukin-4 (rhulL-4) have been evaluated in phase I and phase II studies in human patients with a variety of malignancies. Clinical trials have demonstrated that subcutaneous administration of rhulL-4 is safe and well tolerated at doses as high as 5 μg/kg/day and as high as 10 μg/kg when administered 3 times/week. Although preclinical safety studies in cynomolgus monkeys demonstrated a number of adverse effects following repeated daily dosing with rhulL-4, similar effects have generally not been observed in human patients (Leach et al., 1997). The most common toxicities were elevated liver function tests, nausea/vomiting/diarrhea, malaise/fatigue, edema, headache, myalgias/arthralgias, and fever/chills. Despite promising preclinical growth inhibitory and immunomodulatory effects, IL-4 in this dose and schedule showed only low antitumor activity (Whitehead et al., 1998).
Many human autoimmune and inflammatory diseases are still treated by a combination of corticosteroids and general immunosuppression. A better understanding of the pathogenesis of these diseases has led to therapies that are more specific. Among these, the recombinant humanized proteins are considered as the future therapies. However, drugs based on recombinant proteins have several disadvantages including high production cost, big batch-to-batch variation and denaturation during storage.